Heat exchanger

ABSTRACT

A heat exchanger includes flat tubes and corrugated fins. The corrugated fin includes peak portions contacting the adjacent tubes, and flat portions for making air to pass therebetween in an air flow direction. The flat portion has a first area including pairs of end louvers provided in end portions of the flat portion in a width direction between the adjacent tubes, and a flat part provided between the end louvers in the width direction. The pairs of the end louvers are arranged in the flat portion in the air flow direction. The first area is provided at least one of an upstream end portion and a downstream end portion of the flat portion in the air flow direction.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2006-52092 filed on Feb. 28, 2006, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat exchanger. For example, the heat exchanger can be suitably used for a refrigeration cycle or a heat pump cycle with a defrosting operation.

2. Description of Related Art

When a heat exchanger (e.g., evaporator) is used as an outside heat-exchanging unit in a water heater using a heat pump cycle, frost may be caused on the heat exchanger. In order to eliminate the frost, a defrosting operation is performed for the heat exchanger. While the defrosting operation of the heat exchanger is performed, the heat pump cycle cannot operate normally. Therefore, the defrosting operation is required to be performed in a short time so as to make a normal operation time for the heat pump cycle to be long.

For example, a water-discharging path is secured in a heat exchanger disclosed by JP-A-5-322478, JP-A-9-280754 or JP-A-2001-59690, thereby water generated in the defrosting operation can be rapidly discharged out of the heat exchanger. In the heat exchanger, a hollow or a notch is formed in a connection part between a refrigerant passage tube and a corrugated fin, or an aperture is formed in a flat portion of the corrugated fin. Further, JP-A-9-280754 and JP-A-2001-59690 propose that a groove is formed on a face of the refrigerant passage tube so as to improve a water-discharging performance.

JP-A-2004-101074 discloses another heat exchanger, in which louvers are formed on a flat portion of a corrugated fin. The louver extends in a width direction of the flat portion, and has different angles relative to the flat portion between its center part and its end part. Condensed water can be easily discharged through the, end part of the louver, because the end part of the louver has a larger angle relative to the flat portion than the center part of the louver.

In contrast, in a heat exchanger disclosed by JP-A-6-147785, a corrugated fin is made to protrude from a tube surface toward an upstream side of air flow so as to reduce an amount of frost at the upstream air side on the tube surface.

However, in any heat exchanger described above, a curvature radius of a bending portion between a flat portion and a peak portion of a corrugated fin may affect water-discharging performance. The peak portions are connected to a refrigerant passage tube, and the flat portions between adjacent tubes form air passage. When the curvature radius of the bending portion is large, a clearance between the refrigerant passage tube and the bending portion is large. Thus, water-discharging performance may be lowered, because water easily remains in the clearance.

The curvature radius of the bending portion may not be made smaller in the above-described related arts. This is because a rigidity of the bending portion may not be increased, as long as the corrugated fin is manufactured by a conventional method using a high-speed roller.

SUMMARY OF THE INVENTION

In view of the foregoing and other problems, it is an object of the present invention to provide a heat exchanger having a high water-discharging performance when a defrosting of the heat exchanger is performed. It is a further object of the present invention to improve the water-discharging performance while heat-exchanging performance of the heat exchanger is improved.

According to a first example of the present invention, a heat exchanger includes: a plurality of flat tubes arranged in parallel, each flat tube having a passage therein through which a thermal medium flows in a tube longitudinal direction; and a plurality of corrugated fins, each of which is disposed between adjacent tubes. The corrugated fin includes a plurality of peak portions contacting the adjacent tubes, and a plurality of flat portions for making air to pass therebetween in an air flow direction. Each of the flat portions is bent from the peak portion to be positioned between the adjacent tubes. The flat portion has a first area including a plurality of pairs of end louvers provided in end portions of the flat portion in a width direction between the adjacent tubes, and a flat part provided between the end louvers in the width direction. The pairs of the end louvers are arranged in the flat portion in the air flow direction perpendicular to the width direction and the tube longitudinal direction. The first area is provided at least one of an upstream end portion and a downstream end portion of the flat portion in the air flow direction.

According to a second example of the present invention, a heat exchanger includes: a plurality of flat tubes arranged in parallel, each flat tube having a passage therein through which a thermal medium flows in a tube longitudinal direction; and a plurality of corrugated fins, each of which is disposed between adjacent tubes. The corrugated fin includes a plurality of peak portions contacting the adjacent tubes, and a plurality of flat portions for making air to pass therebetween in an air flow direction. Each of the flat portions is bent from the peak portion to be positioned between the adjacent tubes. The flat portion has a louver area including a plurality of pairs of end louvers provided in end portions of the flat portion in a width direction between the adjacent tubes, and a corresponding number of center louvers provided between the end louvers in the width direction. The pairs of the end louvers are arranged in the air flow direction perpendicular to the width direction and the tube longitudinal direction. The end louver has a predetermined protruding height protruding from the flat portion in the tube longitudinal direction, which is larger than a protruding height of the center louver. The flat portion is bent from the peak portion to have a bending portion therebetween. The bending portion has a curvature radius equal to or smaller than 0.5 mm.

Accordingly, the heat exchanger can have a high water-discharging performance when defrosting of the heat exchanger is performed. Further, it is possible to improve the water-discharging performance while heat-exchanging performance of the heat exchanger is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic perspective view showing a heat exchanger according to a first embodiment of the present invention;

FIG. 2 is an enlarged view showing tubes and corrugated fins of the heat exchanger in FIG. 1;

FIG. 3 is a perspective view showing a part of the corrugated fin;

FIG. 4A is a schematic side view showing a connection part between the tube and the corrugated fin, and FIG. 4B is a schematic side view showing a conventional connection part between a tube and a corrugated fin;

FIG. 5 is a side view showing a part of the corrugated fin;

FIG. 6 is a graph showing a relationship between a height of an end louver and a curvature radius of a bending portion between a flat portion and a peak portion;

FIG. 7 is a graph showing a relationship between a height of an aperture formed in the end louver and a water retention amount;

FIG. 8 is a graph showing a relationship between a height of a center louver and a water retention amount or a frosting time;

FIG. 9 is a schematic view showing a water-discharging path;

FIG. 10 is a perspective view showing a part of a corrugated fin according to a second embodiment;

FIG. 11A is a perspective view showing a part of a corrugated fin according to a third embodiment, and FIG. 11B is a plan view showing the corrugated fin and tubes;

FIG. 12 is a perspective view showing a part of a corrugated fin according to a fourth embodiment;

FIG. 13 is a perspective view showing a part of a corrugated fin according to a fifth embodiment; and

FIG. 14 is a plan view showing a corrugated fin and tubes according to a sixth embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT First Embodiment

FIG. 1 shows a heat exchanger 1, which is suitably used for an outside heat-exchanging unit for a heat pump cycle, for example. As shown in FIGS. 1 and 2, the heat exchanger 1 includes plural flat tubes 2 and plural corrugated fins 3 disposed between the adjacent tubes 2. The tubes 2 are approximately in parallel to each other, and the fins 3 are connected to the tubes 2 to thermally contact the tubes 2. A blower (not shown) sends air 5 into space parts between the fins 3 and the tubes 2.

As shown in FIG. 2, the fin 3 has flat portions 10 and peak portions 11, which are alternately bent. The peak portions 11 are brazed to the tubes 2. A longitudinal direction of the flat portion 10 corresponds to a depth direction D of the fin 3 (i.e., a flow direction of the air 5). The flat portion 10 has louvers 4 (16, 18) extending in a width direction W of the fin 3, which is perpendicular to the fin depth direction D. In this embodiment, the fin depth direction D corresponds to a major direction of the flat tube 2 in cross-section, and the fin width direction W corresponds to a minor direction of the flat tube 2 in cross-section. The louvers 4 (16, 18) will be described below.

The air 5 flows between the flat portions 10 of the fin 3, and a part of the air 5 flows through an aperture formed by the louver 4 (16, 18). At this time, heat is absorbed from or radiated to the air 5, and transmitted to a thermal medium (refrigerant) 7 flowing through a refrigerant passage 6 in the tube 2. Microscopic asperities may be formed on an inner face of the refrigerant passage 6 so as to promote a heat transmission. In this embodiment, plural refrigerant passages 6 extending in a tube longitudinal direction are formed in each tube 2.

A top end of each tube 2 is connected to a top header tank 8 a, and a bottom end of each tube 2 is connected to a bottom header tank 8 b, as shown in FIG. 1. The tanks 8 a, 8 b are provided with an inlet or outlet for the medium 7 in the heat exchanger 1. A side board 9 is arranged on each end of the heat exchanger 1 in the width direction W so as to protect the fins 3.

When the heat pump cycle is actuated, the air 5 sent toward the heat exchanger 1 is cooled while passing through the spaces of the fin 3, because the refrigerant 7 in the tube 2 absorbs radiant heat of the air 5 through the peak portion 11 of the fin 3. That is, the tube 2 operates as an evaporator in which the refrigerant 7 is evaporated.

Thus, moisture in the air 5 becomes in a saturated state. When a temperature of a wall of air passage, constructed with the tube 2 and the fin 3, is equal to or lower than 0° C., the saturated moisture frosts on the wall. Further, when the frost is increased, the air passage is closed with the frost. At this time, the heat pump cycle is switched from a normal operation to a defrosting operation so as to remove the frost on the heat exchanger 1. After the frost formed in the air passage of the heat exchanger 1 is melted, the heat pump cycle performs again the normal operation.

Here, a normally operating time period of the heat pump cycle is defined as a frosting time for which the heat exchanger 1 is operated as an evaporator, and a defrosting time period of the heat pump cycle is defined as a defrosting time for which the defrosting of the heat exchanger 1 is performed. In order to shorten the defrosting time, water melted for the defrosting time is required to be rapidly discharged out of the heat exchanger 1.

FIG. 3 is a perspective view showing a part of the fin 3, before connected to the tube 2. The fin 3 is typically formed by using a fin-forming apparatus (not shown) with a high-speed roller. The flat portion 10 and the peak portion 11 are connected through a bending portion 12. A curvature radius R of an inner side 12 a of the bending portion 12 is set equal to or smaller than 0.5 mm. Favorably, the curvature radius R may be set equal to or smaller than 0.3 mm. The curvature radius R will be described below.

The peak portion 11 has a flat part, i.e., flat tip FT. As shown in FIG. 4A, the peak portion 11 and the tube 2 are brazed such that the flat part of the peak portion 11 is in contact with a flat face of the tube 2. Thereby, a thermal contact between the tube 2 and the fin 3 can be secured.

Further, a clearance 12 b between the bending portion 12 of the fin 3 and the tube 2 is small, because the curvature radius R is equal to or smaller than 0.5 mm. Therefore, the clearance 12 b can be easily filled with a small amount of a brazing material 19. Even if the clearance 12 b cannot completely be filled with the brazing material 19, an amount of water kept in the clearance 12 b can be reduced, because the clearance 12 b is too small to keep water.

In contrast, as shown in FIG. 4B, the curvature radius R of the bending portion 12 is large in a conventional art. In this case, the brazing material 19 cannot fill all of the clearance 12 b between the bending portion 12 of the fin 3 and the tube 2, because the curvature radius R of the bending portion 12 is too large. Thus, the amount of water kept in the clearance 12 b may be increased, because water 20 generated in the defrosting operation easily stays on the brazing material 19 in the clearance 12 b, as shown in FIG. 4B.

As shown in FIG. 3, the flat portion 10 has an end louver area A1 and two full louver areas B1, B2 thereon, for example. The end louver area A1 and the full louver area B1 are positioned relatively on an upstream air side of the flat portion 10 in this order, and the other full louver area B2 is positioned relatively on a downstream air side of the flat portion 10. The upstream air side and the downstream air side are separated at an approximately center part of the flat portion 10 in the depth direction D (air flow direction). The end louver area A1 and the full louver areas B1, B2 are defined as a louver-formed area.

In the end louver area A1, a pair of end louvers 16 is formed on end portions of the flat portion 10 in the width direction W. As shown in FIG. 5, the end louver 16 has a protruding height h1 protruding from the flat portion 10, and an aperture 16 c formed by the end louver 16 has an aperture height h2. As shown in FIG. 3, plural (e.g., four) pairs of the end louvers 16 are arranged in the depth direction D of the end louver area A1. The end louver area A1 further has a flat (non-louver) part 17 on the flat portion 10 between the pairs of the end louvers 16 in the width direction W.

In contrast, in the full louver area B1, B2, a center louver 18 extends in the width direction W of the flat portion 10, and is successively connected to a pair of the end louvers 16 in the width direction W. That is, the pair of the end louvers 16 and the center louver 18 are continuously formed in the width direction D. Plural (e.g., twelve=four in the full louver area B1+eight in the full louver area B2) sets of the first louvers 16 and the pairs of the second louvers 18 are arranged on the full louver areas B1, B2 in the depth direction D of the flat portion 10.

When the louver 16, 18 in the upstream side (areas A1 and B1) of the flat portion 10 has an angle θ1 relative to the flat portion 10, and when the louver 16, 18 in the downstream side (area B2) of the flat portion 10 has an angle θ2 relative to the flat portion 10, the angles θ1, θ2 are symmetrical about a dashed line 14 (i.e., θ1=−θ2). The dashed line 14 represents an approximately central line of the flat portion 10 in the depth direction D.

As shown in FIG. 5, the height h1 of the end louver 16 represents a maximum protruding dimension from a louver-side face 10 a of the flat portion 10 to an outer face 16 a of the end louver 16 in the tube longitudinal direction, and a protruding height h3 of the center louver 18 represents a maximum protruding dimension from a louver-side face 10 a of the flat portion 10 to an outer face 18 a of the center louver 18 in the tube longitudinal direction. The height h1 of the end louver 16 is larger than the height h3 of the center louver 18 (i.e., h1>h3). Therefore, each of the ends of the center louver 18 is connected to the end louver 16 in the width direction W such that the height h1 of the end louver 16 is larger than the height h3 of the center louver 18.

Further, the height h2 of the aperture 16 c formed by the end louver 16 represents a maximum aperture dimension from the louver-side face 10 a of the flat portion 10 to an inner face 16 b of the end louver 16 in the tube longitudinal direction, in which the inner face 16 b is opposite to the outer face 16 a. When the height h2 is larger than 0 mm, the aperture 16 c is open toward the upstream air side of the flat portion 10. In contrast, when the height h2 is smaller than 0 mm, the aperture 16 c is open toward the downstream air side of the flat portion 10. When the height h2 is equal to 0 mm, the end louver 16 is protruded from the louver-side face 10 a by a thickness of the end louver 16. A shape of the aperture 16 c is formed into a trapezoid, as shown in FIG. 5.

Next, characteristics of the heights h1, h2, h3 will be described. As shown in FIG. 6, when the height h1 of the end louver 16 is equal to or larger than 0.1 mm, the curvature radius R of the bending portion 12 between the peak portion 11 and the flat portion 10 can be made to be about 0.3 mm. In contrast, when the height h1 is smaller than 0.1 mm, the curvature radius R is required to be made larger, as the height h1 is made smaller.

That is, when the height h1 of the end louver 16 is equal to or larger than 0.1 mm, rigidity of the flat portion 10 around the end louver 16 can be enhanced, thereby the curvature radius R can be made smaller. Therefore, the height h1 of the end louver 16 is made to be equal to or larger than 0.1 mm in order to reduce the water retention amount in the clearance 12 b.

As shown in FIG. 7, when the height h2 of the aperture 16 c formed by the end louver 16 is equal to or larger than 0 mm, water on the flat portion 10 can be smoothly discharged through the aperture 16 c. Thus, the water retention amount on the flat portion 10 can be reduced.

As shown in FIG. 8, when the height h3 of the center louver 18 is made larger, frost generates more easily, because heat-exchanging amount between the fin 3 and the air 5 becomes larger. That is, the frosting time becomes shorter, as the height h3 of the center louver 18 is made larger.

In contrast, water 20 on the flat portion 10 can be easily moved through the center louver 18, as shown in FIG. 9. As long as the center louver 18 is slightly formed, the water 20 on the flat portion 10 can move toward the end louver 16 through the center louver 18 due to a capillary force of the center louver 18. After the water 20 moves through the center louver 18 to the end louver 16, the water 20 passes through the aperture 16 c. Then, the water 20 gathers in the clearance 12 b between the tube 2 and an adjacent (lower) flat portion 10. The water 20 moves in the depth direction D due to a capillary force of the clearance 12 b, and is discharged out of the fin 3.

As shown in FIG. 8, when the height h3 of the center louver 18 is larger than 0 mm (h3>0), water on the flat portion 10 can be moved toward the end louver 16 through the center louver 18. Then, water passes through the aperture 16 c of the end louver 16. Thereby, the water retention amount on the flat portion 10 can be reduced.

Here, the height h3 of the center louver 18 is required to be made smaller, because the frosting time (normally operating time of the heat pump cycle) becomes shorter as the height h3 of the center louver 18 is made larger. Therefore, the height h3 of the center louver 18 is made equal to or smaller than 0.1 mm, in view of a manufacturing variation (error). Alternatively, the height h3 of the center louver 18 may be made equal to or smaller than 0.15 mm.

In contrast, the center louvers 18 are not arranged on the end louver area A1, as shown in FIG. 3, due to a balance between the frosting time and the water-discharging performance. That is, the flat part 17 is arranged on a position corresponding to a position for the center louvers 18 in the end louver area A1, because an amount of frost is generally large at the upstream air side of the flat portion 10.

According to the first embodiment, the height h1 of the end louver 16 is equal to or larger than 0.1 mm, and the height h2 of the aperture 16 c formed by the end louver 16 is equal to or larger than 0 mm. The height h3 of the center louver 18 is equal to or smaller than 0.1 mm, and the curvature radius R is set to be about 0.3 mm.

Thus, in the end louver area A1, the flat part 17 reduces an amount of frost, and the end louvers 16 improve the water-discharging performance. Because of the end louvers 16, water can be easily discharged through the apertures 16 c of the end louvers 16. Further, water can easily move along the bending portion 12 in the depth direction D between the tube 2 and the fin 3, because the curvature radius R is made smaller due to the large height h1 of the end louver 16.

In contrast, in the full louver area B1, B2, the center louver 18 can operate as a water-discharging path toward the ends of the flat portion 10 in the width direction W. Because the height h3 of the center louver 18 is made smaller, the frosting time of the heat exchanger 1 can be made longer. Furthermore, the end louvers 16 in the full louver areas B1 and B2 improve the water-discharging performance, similarly to the end louver area A1.

The end louver area A1 is suitably used for a position, at which a heat-exchanging performance is less required, and the full louver areas B1, B2 are suitably used for a position, at which a heat-exchanging performance is more required.

In addition, a ratio of the defrosting time to an entire operating time (i.e., a sum of the frosting time and the defrosting time) is 19% in the heat exchanger 1 of the first embodiment, while the ratio in the comparative heat exchanger shown in FIG. 4B is 26%. Further, an average coefficient of performance (COP) of the heat exchanger 1 is improved by 9%, compared with that of the comparative heat exchanger shown in FIG. 4B. The COP represents a ratio of output heating performance to input electricity in the heat pump cycle.

Thus, efficiency for the defrosting operation can be increased, because the amount of frost is reduced, and because the water-discharging performance of melted ice (frost) is improved. Accordingly, the defrosting time can be reduced.

Second Embodiment

As shown in FIG. 10, only end louver areas A1, A2 are arranged on a flat portion 10 in a second embodiment. That is, the end louver area A1 is positioned at an upstream air side of the flat portion 10, and the end louver area A2 is positioned at a downstream side of the flat portion 10. Eight pairs of end louvers 16 are arranged on the end louver area A1, A2, and a flat (non-louver) part 17 is disposed between the end louvers 16 in the width direction W. The angle of the end louvers 16 relative to the flat portion 10 in the area A1 is opposite to that in the area A2. The other parts are made similar to the first embodiment.

According to the second embodiment, frost formed on the flat portion 10 can be reduced due to the flat part 17 without a louver. Therefore, the frosting time for normally operating the heat pump cycle can be relatively increased.

Further, the end louvers 16 are arranged in the depth direction D approximately from an upstream end 13 to a downstream end 15 on the flat portion 10. Actually, the end louvers 16 are provided to be slightly spaced from the upstream end 13 and downstream side 15. Thus, the water-discharging performance can be improved, because water can be easily discharged through the apertures 16 c of the end louvers 16, and because water can easily move along the clearance 12 b with the small curvature radius R in the depth direction D between the tube 2 and the fin 3.

Third Embodiment

As shown in FIG. 11B, a dimension of a corrugated fin 3 in the depth direction D is longer than that of a tube 2 in a third embodiment. A downstream end 15 of the fin 3 corresponds to a downstream end of the tube 2, and an upstream end 13 of the fin 3 is protruded from an upstream end 22 of the tube 2 toward the upstream air side so as to form a protrusion 21. The protrusion 21 is formed by extending the flat portion 10, and has a flat (non-louver) part 17 thereon. Any end louver 16 is not arranged on the protrusion 21, because the protrusion 21 is not in contact with the tube 2.

As shown in FIG. 11A, an end louver area A2 is positioned at a downstream air side on the flat portion 10, and two full louver areas B1, B2 are positioned between the end louver area A2 and the flat part 17 (protrusion 21).

A height h1 of the end louver 16, a height h2 of an aperture formed by the end louver 16 and a height h3 of a center louver 18 are made similar to the first embodiment. For example, four pairs of the end louvers 16 are formed on the end louver area A2, and four pairs of the end louvers 16 and four center louvers 18 are formed on each of the full louver areas B1, B2.

According to the third embodiment, appropriate fin efficiency can be provided at the upstream air side of the flat portion 10 by the full louver area B1, while an amount of frost is reduced at the upstream air side of the flat portion 10 by the protrusion 21. Thus, the frosting time can be made longer.

In contrast, because the amount of frost is made small at the downstream air side, the center louver 18 is not arranged around the downstream end 15. However, the end louver 16 can effectively improve the water-discharging performance around the downstream end 15 due to the aperture 16 c, and is effective for making the curvature radius R smaller due to the large height h1.

Fourth Embodiment

As shown in FIG. 12, only full louver areas B1, B2 are arranged on a flat portion 10 in a fourth embodiment. That is, the full louver area B1 is positioned at an upstream air side of the flat portion 10, and the full louver area B2 is positioned at a downstream air side of the flat portion 10. Eight pairs of end louvers 16 and eight center louvers 18 are arranged on each of the full louver areas B1, B2. The other parts may be made similar to the first embodiment.

According to the fourth embodiment, the louvers 16, 18 are arranged to be symmetrical with respective to the dashed line 14. Therefore, performance for manufacturing the fins 3 with a high-speed roller can be improved, because a rigidity of the flat portion 10 is uniform. In addition, the full louver areas B1, B2 in the fourth embodiment provide the same advantages, as the above embodiments.

Further, the frosting time can be made longer, because the height h3 of the center louver 18 is made smaller, while the amount of frost is increased by the center louver 18 compared with the flat part 17, especially at the upstream side of the flat portion 10.

Fifth Embodiment

As shown in FIG. 13, an end louver area A1, a full louver area B1, the full louver area B2 and the end louver area A2 are arranged in this order from an upstream end 13 to a downstream end 15 on the flat portion 10. The other parts may be made similar to the first embodiment.

According to the fifth embodiment, the louvers 16, 18 are arranged to be symmetrical with respect to the dashed line 14. Therefore, performance for manufacturing the fins 3 with a high-speed roller can be improved, because a rigidity of the flat portion 10 is uniform. In addition, the end louver areas A1, A2 and the full louver areas B1, B2 in the fourth embodiment provide the same advantages as the above embodiments.

Further, the flat (non-louver) part 17 is arranged adjacent to the upstream end 13. Thus, the frosting time can be effectively increased, because an amount of frost can be reduced due to the flat part 17.

Sixth Embodiment

As shown in FIG. 14, a dimension of a corrugated fin 3 in the depth direction D is longer than that of a tube 2 in a sixth embodiment. An upstream end 13 of the flat portion 10 is protruded from an upstream end 22 of the tube 2 so as to form a protrusion 21. The protrusion 21 is formed by extending the flat portion 10, and has an end louver area A1 thereon. Therefore, the protrusion 21 has pairs of end louvers 16 and a flat (non-louver) part 17 thereon. Thereby, the frosting time can be made longer, because an amount of frost can be decreased on the protrusion 21 due to the flat part 17. The end louvers 16 do not affect the amount of frost, and improves water-discharging performance.

Moreover, plural (e.g., four) grooves 23 are formed on a face of the tube 2 in the sixth embodiment. The groove 23 extends in approximately parallel to the refrigerant passage 6, and is positioned so as to intersect the peak portion 11. Therefore, the clearance 12 b between the tube 2 and the bending portion 12 of the fin 3 also intersects the groove 23.

After water generated in the defrosting operation moves toward the end louver 16 through the center louver 18, water passes through the aperture 16 c of the end louver 16. Then, water moves toward the groove 23 in the depth direction D using a capillary force by the clearance 12 b, and is discharged out of the heat exchanger 1 through the groove 23.

According to the sixth embodiment, the water-discharging performance can be more improved due to the groove 23. In addition, the end louver area A1 and the full louver areas B1, B2 in the sixth embodiment provide the same advantages as the above embodiments.

Other Embodiments

The curvature radius R of the bending portion 12 between the tube 2 and the fin 3 is set to 0.3 mm in the first embodiment. However, the curvature radius R may be in a range between 0.1 mm and 0.5 mm, in view of a manufacturing variation. In a case in which the curvature radius R is set to 0.5 mm, water-discharging performance can be improved compared with a heat exchanger having a large curvature radius R, while the clearance 12 b between the bending portion 12 of the fin 3 and the tube 2 is large.

The height h3 of the center louver 18 is equal to or smaller than 0.1 mm in the first embodiment. However, the height h3 may be set equal to or smaller than 0.15 mm, in view of a manufacturing variation.

The aperture 16 c of the end louver 16 is shaped into a trapezoid. Alternatively, the aperture 16 c may be shaped into a semicircle, a semielliptic or a polygon, e.g., triangle or quadrangle. In this case, definitions of the heights h1, h2 are made similar to those shown in FIG. 5.

The aperture 16 c is open toward the upstream air side of the flat portion 10 in the louver areas A1, B1, and the aperture 16 c is open toward the downstream air side of the flat portion 10 in the louver areas A2, B2. However, the aperture 16 c may be open toward the same side of the flat portion 10 in the louver areas A1, B1, A2, B2.

In the above-described embodiments, each of the flat portions 10 can be bent from the peak portion 11 by approximately 90°.

Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims. 

1. A heat exchanger comprising: a plurality of flat tubes arranged in parallel, each flat tube having a passage therein through which a thermal medium flows in a tube longitudinal direction; and a plurality of corrugated fins, each of which is disposed between adjacent tubes, wherein the corrugated fin includes a plurality of peak portions contacting the adjacent tubes, and a plurality of flat portions for making air to pass therebetween in an air flow direction, each of the flat portions is bent from the peak portion to be positioned between the adjacent tubes, the flat portion has a first area including a plurality of pairs of end louvers provided in end portions of the flat portion in a width direction between the adjacent tubes, and a flat part provided between the end louvers in the width direction, the pairs of the end louvers are arranged in the flat portion in the air flow direction perpendicular to the width direction and the tube longitudinal direction, and the first area is provided at least one of an upstream end portion and a downstream end portion of the flat portion in the air flow direction.
 2. The heat exchanger according to claim 1, wherein: the first area is provided on the flat portion from the upstream end portion to the downstream end portion in the air flow direction.
 3. The heat exchanger according to claim 1, wherein: the flat portion further has a second area including the pairs of the end louvers, and a corresponding number of center louvers; and each center louver and a pair of the end louvers are successively connected in the width direction.
 4. The heat exchanger according to claim 3, wherein: the end louver has a protruding height protruding from the flat portion, which is larger than a protruding height of the center louver.
 5. The heat exchanger according to claim 4, wherein: the protruding height of the end louver is equal to or larger than 0.1 mm, which is a dimension between a louver-side face of the flat portion and an outer face of the end louver in the tube longitudinal direction; and the end louver has an aperture having a height dimension between the louver-side face of the flat portion and an inner face of the end louver in the tube longitudinal direction, the height dimension being equal to or larger than 0 mm.
 6. The heat exchanger according to claim 1, wherein: the tube has a groove thereon extending approximately in parallel to the tube longitudinal direction; and the peak portion is connected to the tube so as to intersect the groove.
 7. The heat exchanger according to claim 1, wherein: the flat portion includes a protrusion protruding from an upstream end of the tube in the air flow direction.
 8. The heat exchanger according to claim 7, wherein: the protrusion has only a flat part thereon.
 9. The heat exchanger according to claim 7, wherein: the protrusion has a plurality of pairs of the end louvers on the end portions in the width direction.
 10. The heat exchanger according to claim 1, wherein: the flat portion is bent from the peak portion to have a bending portion therebetween; and the bending portion has a curvature radius equal to or smaller than 0.5 mm.
 11. The heat exchanger according to claim 10, wherein: the curvature radius is equal to or smaller than 0.3 mm.
 12. The heat exchanger according to claim 10, wherein: the flat portion includes a plurality of center louvers, each center louver being connected to the pair of end louvers in the width direction and having a protruding height protruding from the flat portion; and the protruding height of the center louver is equal to or smaller than 0.15 mm, which is a dimension between a louver-side face of the flat portion and an outer face of the center louver in the longitudinal direction.
 13. The heat exchanger according to claim 12, wherein: the protruding height of the center louver is equal to or smaller than 0.1 mm.
 14. A heat exchanger comprising: a plurality of flat tubes arranged in parallel, each flat tube having a passage therein through which a thermal medium flows in a tube longitudinal direction; and a plurality of corrugated fins, each of which is disposed between adjacent tubes, wherein the corrugated fin includes a plurality of peak portions contacting the adjacent tubes, and a plurality of flat portions for making air to pass therebetween in an air flow direction, each of the flat portions is bent from the peak portion to be positioned between the adjacent tubes, and to have a bending portion between the flat portion and the peak portion the flat portion has a louver area including a plurality of pairs of end louvers provided in end portions of the flat portion in a width direction between the adjacent tubes, and a corresponding number of center louvers provided between the end louvers in the width direction, the pairs of the end louvers are arranged in the air flow direction perpendicular to the width direction and the tube longitudinal direction, the end louver has a predetermined protruding height protruding from the flat portion in the tube longitudinal direction, which is larger than a protruding height of the center louver, and the bending portion has a curvature radius equal to or smaller than 0.5 mm.
 15. The heat exchanger according to claim 14, wherein: the curvature radius is equal to or smaller than 0.3 mm.
 16. The heat exchanger according to claim 14, wherein: the peak portion is a flat part in contact with the tube.
 17. The heat exchanger according to claim 14, wherein: the protruding height of the center louver is equal to or smaller than 0.15 mm, which is a dimension between a louver-side face of the flat portion and an outer face of the center louver in the longitudinal direction.
 18. The heat exchanger according to claim 17, wherein: the protruding height of the center louver is equal to or smaller than 0.1 mm.
 19. The heat exchanger according to claim 14, wherein: the tube has a groove thereon extending approximately in parallel to the tube longitudinal direction; and the peak portion is connected to the tube so as to intersect the groove.
 20. The heat exchanger according to claim 14, wherein: the flat portion is bent from the peak portion by approximately 90°. 